22.19Tritone substitution doesn't always fit the melody

Suppose melody over G7 is:

G

Replace G7 with D♭7.

G is:

#11 of D♭7.

That might sound great.

But it is more colorful than before.

If melody is D:

over D♭7, D becomes ♭9.

Much stronger tension.

So always check the melody.